Monday, 20 August 2012

Serendipity

My photography sessions are dominated mostly by the weather, and even when the weather is half-reasonable I can still struggle to get half a dozen decent shots. Sometimes, however, everything clicks and I manage to get a good range of illustrative images.

Scaeva pyrastri is a hoverfly that can be readily identified by the abdominal markings: they are paler than most species and the inner part of the curve is further forward than the outer part. In this shot, you can also see the hairy eyes, which separate it from other similar species.

Scaeva pyrastri hoverfly
Scaeva pyrastri is thought to be immigrant from mainland Europe, and I know that there has been a mass migration of moths to Ireland in the past couple of days, so this hoverfly has almost certainly flown from France to breed here. (The brown hoverfly at top left is Eristalis pertinax).

Eristalis intricarius is one of our best bumblebee-mimicking hoverflies:

The bumblebee mimicking hoverfly Eristalis intricarius
That yellow/orange 'band' is very convincing in life, but when you see it close-up, it's clearly just a scutellum with longer than usual hairs.

And just as I was standing up from taking that shot, I saw the very bumblebee that it is mimicking:

Bombus lucorum (agg) (right) and Bombus pascuorum (left, both workers)
That's a nice shot of two of my 6 local bumblebee species.

Helophilus pendulus is perhaps the most common single species of hoverfly on the patch at the moment. I know that there are a few related (but rarer) species that might be around, so I examine each specimen very carefully just in case. Today I got that 'eureka' moment as I found this male Helophilus hybridus:

Helophilus hybridus (male)
Helophilus hybridus larvae are associated with black mud where Bulrush is present, and the adults don't disperse very far. There is a stand of Bulrush about 300m. from where this shot was taken.

Here's an archive shot of Helophilus pendulus for comparison:

Helophilus pendulus (archive)
Notice that the yellow abdominal markings are quite different, and the rear legs are yellow only at the 'knee' in hybridus, but the yellow is extensive on pendulus.

The larvae of some fly and micromoth species feed on the seeds of composite flowers such as Knapweed. The seeds are an excellent food source, and the larvae can feed inside the undeveloped seedheads in relative safety.

Notice the word 'relative'; some parasitic wasps are aware that there are larvae inside the flowerhead, and at the appropriate time (now) we can see the Ichneumonids searching the unopened flowerheads. When a larva is detected, the ovipositor is deployed and we see the drilling operation that takes place:

Ichneumonid ovipositing in larvae inside the Knapweed flowerhead
The eggs are deposited inside the body of the hidden larva and will remain there until the larva has reached full size. At this time (or soon after the larva has pupated) the ichneumonid egg hatches out and the ichneumonid larva eats the host before pupating inside the husk. This egg-laying process can be seen in perhaps three days per year.

Here's an unusual shot of the process from the rear:

Ichneumonid ovipositing

A few days ago, I showed a picture of a very atypical Square-spot Rustic. Here's one that looks as if it has read the book and followed the rules:

Square-spot Rustic
Here's a link to the original post, for comparison.


4 comments:

Gill said...

Fantastic pics - I shall have to inspect my Helophilus more carefully near the bulrushes (by which do you mean Typha or - they're everywhere just now.

Isn't' that Eristalis intricarius lovely?

How on earth did you id that original Square-spot Rustic? Apart from the shape it looks nothing like the new one - even the fringe round the edge of the wings is much less obvious.

stuart dunlop said...

Gill: I meant Typha. When I started this identification lark, the convention was that Typha was incorrectly called 'Bulrush', whereas that common name really belonged to Scirpus. But now it seems that 'Bulrush' is fine for either. Just shows the dangers in using common names rather than formal binominals. Typha is essential for quite a number of insects. Other hoverflies and some moths feed on it exclusively. Bulrush Wainscot comes to mind...

I didn't identify the first S-s R, I had to 'call a friend' (who had to call another friend) on that one. But I did identify the second one (and quite a few other similar specimens which I have seen in the past week or so). Some moths are identified by the 'elimination rule': you eliminate all things it can't be, and then make sure that what IS there doesn't conflict with what is missing for another positive identification. "I can't see anything else it could possibly be" is a fairly regular phrase on moth forums.

damselfly said...

Ichneumons are amazing insects.

Andrea Devos said...

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